1. Field of the Invention
The present invention relates to a power supply apparatus for generating a plurality of output voltages from one power supply.
2. Description of the Related Art
An automobile is provided with an AC motor, etc. for driving a compressor for an airconditioner, and requires a power supply circuit for generating an AC voltage for driving the AC motor. It also requires a power supply circuit for providing a power supply for a lamp, car stereo, etc.
Recently, a hybrid car has been developed for practical use by combining a gasoline engine and an electric motor to solve the problem of air pollution by exhaust gases. The hybrid car also requires a power supply circuit for driving a motor for running the car.
Normally, since the voltage for a motor is different from the voltage for a lamp, etc., one battery voltage is converted into different AC voltages using two inverters, and the AC voltages are further converted into a DC voltage as necessary.
FIG. 1 shows the configuration of the conventional power supply circuit and AC motor. An inverter 11 is a DC/AC converter for converting a DC voltage of a battery 12 into a 3-phase AC voltage, and is configured by connecting in parallel 3 sets of two serially connected transistors. A U-phase coil of a 3-phase AC motor 13 is connected to the connection point of transistors Q1 and Q2, a V-phase coil of the 3-phase AC motor 13 is connected to the connection point of transistors Q3 and Q4. A W-phase coil is connected to the connection point of the transistors Q5 and Q6.
Furthermore, the voltage of the battery 12 is converted into a desired AC voltage by another inverter circuit 14, supplied to the primary side of a transformer 15, rectified by a rectifier circuit 16 connected to the secondary side, and supplied to a load.
The above mentioned conventional power supply circuit requires two inverters, that is, the inverter 11 for generating an AC voltage to be supplied to the 3-phase AC motor 13, and the inverter circuit 14 for generating the voltage to be supplied to the load of a lamp, etc. As a result, the configuration of the power supply circuit is complicated, thereby causing the problem of increased weight and higher cost.
The present invention aims at realizing a power supply apparatus capable of supplying a plurality of output voltages in a simple configuration.
According to an aspect of the present invention, the power supply apparatus includes: an AC voltage generation unit for generating a polyphase AC voltage; a transformer connected to the neutral point of windings of the AC motor supplied with the AC voltage by said AC voltage generation unit; and a control unit for determining the voltage on the primary side of the transformer by shifting the phase of the voltage of at least one phase of polypase AC voltage generated by the AC voltage generation unit.
According to the invention, by shifting the phase of the polyphase AC voltage, the output voltage of the transformer connected to the neutral point of the AC motor can be changed. Thus, for example, a desired voltage can be supplied to a load without a circuit for adjusting the output voltage on the secondary side of the transformer. Thus, since it is not necessary to provide an inverter circuit, etc. for generating a voltage to be supplied to a load, the configuration of the circuit of the power supply apparatus can be simplified.
In the above mentioned invention, the power supply apparatus includes a DC supply which connects to the input side of the AC voltage generation unit, wherein the AC voltage generation unit includes an inverter circuit which includes a plurality of semiconductor devices, and converts the output voltage of the DC supply into a 3-phase AC voltage.
In the above mentioned invention, one end of the coil on the primary side of the transformer can be connected to the neutral point while the other end can be connected to the earth of the DC supply through the capacitor.
With the configuration, the DC can be prevented from flowing into the transformer, and a smaller transformer can be realized using a small core.
In the above mentioned invention, one end of the coil on the primary side of the transformer can be connected to the neutral point through the capacitor while the other end can be directly connected to the earth of the DC supply.